Central D2-dopamine receptor occupancy in relation to antipsychotic drug effects: a double-blind PET study of schizophrenic patients.

The relationship between central D2-dopamine receptor occupancy and antipsychotic drug effects was examined in a double-blind study. Raclopride was the compound used to induce a selective occupancy of the D2-dopamine receptors. In addition, 11C-labeled raclopride was the radioligand used to measure occupancy by positron emission tomography (PET). Seventeen schizophrenic patients were randomly assigned to one of three parallel groups treated for 4 weeks with daily doses of 2, 6, or 12 mg of raclopride. D2-receptor occupancy was determined by PET at steady-state conditions in 13 patients who completed the study. A statistically significant relationship was demonstrated between antipsychotic effect and degree of D2-receptor occupancy (p < 0.05). Patients with extrapyramidal side effects had significantly higher D2-receptor occupancy than those without (p = 0.02). The finding of a relationship between selective occupancy of the D2-dopamine receptors and clinical effects in schizophrenic patients principally provides new support for the dopamine hypothesis of antipsychotic drug action.

An open label trial of raclopride in acute schizophrenia. Confirmation of D2-dopamine receptor occupancy by PET.

Raclopride, a highly selective D2-dopamine receptor antagonist, was administered in doses up to 4 mg b.i.d. to ten schizophrenic patients in an open label non-comparative study lasting 4 weeks. Safety, tolerability, potential antipsychotic effect, prolactin response and drug effect on plasma homovanillic acid were evaluated. Central D2-dopamine receptor occupancy was determined by positron emission tomography (PET). No major deviations were found in biochemical and physiological safety parameters. Raclopride was well tolerated. The mean BPRS score was reduced by 55% at endpoint. In the global evaluation seven patients were "very much" or "much" improved. Extrapyramidal side effects were recorded in four patients and disappeared after dose reduction or single doses of biperiden. An increase in plasma prolactin of short duration was observed in both sexes. A significant decrease of plasma HVA was obtained after 4 weeks of treatment. In two of the patients the central D2-dopamine receptors occupancy was measured using PET. The receptor occupancy was 68 and 72% which is the same as that found in patients treated with conventional neuroleptics.

An open study of the pharmacokinetics and the tolerability of raclopride extended release capsules in psychiatric patients.

Following a 4-7 day drug-free washout period, eight male inpatients took an extended-release (ER) formulation of raclopride. After the initial 8 mg dose on day 1 of the study, repeated plasma samples were collected over the ensuing 36 h. Subsequently, patients received raclopride 8 mg b.i.d. through day 7, 12 mg b.i.d. through day 14, and, if tolerated, 16 mg b.i.d. through day 21. On days 7, 14, and 21, repeated plasma samples were drawn over the 12 h following the morning dose. Relative to the previously studied immediate release form of raclopride, the ER formulation delayed and extended the absorption of raclopride, and produced lower maximum raclopride concentrations. Linear kinetics were preserved across the dose range studied. Two patients could not tolerate the highest raclopride dose because of extrapyramidal side effects.

Efficacy, safety and tolerability of raclopride, a specific D2 receptor blocker, in acute schizophrenia: an open trial.

Fifteen acutely ill patients (8 male, 7 female) aged 19 to 63 who met DSM-III criteria for schizophrenic disorder or schizophreniform disorder participated in a 4-week open trial of raclopride. The starting dose of raclopride was 2 mg increasing to 4 mg twice daily in the first week, further increments to 6 mg twice daily at day 14, and 8 mg twice daily at day 21 depending on response. Weekly assessments were made using the BPRS, Montgomery Schizophrenia Scale, Krawiecka-Goldberg Scale and Clinical Global Impression Scale. Extra-pyramidal symptoms and other side-effects were recorded weekly. Four patients failed to complete. Two were withdrawn because of clinical deterioration, and 2 others left hospital against advice after 2 weeks having shown initial improvement. Of the 11 completers, 4 were very much improved and 6 much improved; one was minimally worse. Extra-pyramidal symptoms were infrequent: 3 patients expressed occasional mild akathisia. Six patients complained of mild drowsiness. No major deviations were found in biochemical and physiological safety parameters. Plasma concentrations of raclopride were stable throughout treatment or proportional to dose changes. There was approximately a 6-fold inter-individual difference in steady-state drug concentrations. Plasma levels of prolactin increased transiently after raclopride intake to a maximum of up to 80 and 130 ng/ml in male and female patients respectively.

An open study of tolerability and pharmacokinetics of raclopride extended release capsules in psychiatric patients: a Canadian study.

The tolerability and pharmacokinetics of raclopride extended release (ER) capsules have been evaluated after a single oral dose and at steady state, with 3 different daily doses in 4 male patients requiring neuroleptic treatment. In this 3-week open study, the drug was administered to patients in increasing bid doses of 8 mg, 12 mg and 16 mg, respectively, for each 1-week treatment period, following a 1-week placebo washout. With this limited number of patients, assessments of clinical chemistry, hematology, cardiovascular variables and adverse symptoms suggest that raclopride is safe and well-tolerated in the group studied. The administration of repeated doses of raclopride showed linear pharmacokinetics based on parameter values which are either constant (effective elimination half-life, total plasma clearance, and dose-normalized area under the plasma concentration-time curve) or varying proportionally (trough plasma concentration, peak plasma concentration, average plasma concentration and the area under the plasma concentration-time curve for a dosage interval at steady state) with the doses. The linear 1-compartment open model with zero-order absorption was the most appropriate pharmacokinetic model describing the raclopride plasma concentration profile after a single 8 mg dose of raclopride ER capsules. The ER formulation reduced the fluctuation between peak and trough plasma drug concentrations which has been reported before with instant release dosage forms. In this study, the increase of plasma prolactin concentrations above the normal limit was transient and returned to normal levels. Although the plasma prolactin concentration tended to increase with the drug dose, no direct relationship between raclopride dose and prolactin plasma concentrations was found. The correlation of plasma prolactin response with the plasma raclopride concentration showed a low level of hysteresis.